cat conCATenates one or more files given as argument and prints those on the standard output (console).
If no file or ‘-‘ (dash) is given, it reads from standard input until EOF (Ctrl+D) is pressed and prints is to standard output.

$ ls -l linus # ls to make sure file exists
-rw-rw-r-- 1 daniel daniel 403 Apr 15 01:20 linus
$ cat linus # print content of file to stdout
Hello everybody out there using minix -
I'm doing a (free) operating system (just a hobby, won't be big and professional like gnu) for 386(486) AT clones.
This has been brewing since april, and is starting to get ready.
I'd like any feedback on things people like/dislike in minix,
as my OS resembles it somewhat (same physical layout of the file-system (due to practical reasons) among other things).
$ cat -n linus # show line numbers with -n
1 Hello everybody out there using minix -
2
3 I'm doing a (free) operating system (just a hobby, won't be big and professional like gnu) for 386(486) AT clones.
4 This has been brewing since april, and is starting to get ready.
5 I'd like any feedback on things people like/dislike in minix,
6 as my OS resembles it somewhat (same physical layout of the file-system (due to practical reasons) among other things).
$ cat # read from stdin(keyboard) and print to stdout(screen), repeats after me until I press Ctr+D to end it.
reading
reading
from standard inpu
from standard inpu
pressing Ctr+D now
pressing Ctr+D now
$ cat << EOF > file-from-stdin # Reads from keyboard until EOF is pressed and saves(redirects) the text to a file.
I read this from stdin
end of file
EOF
$ ls -l file-from-stdin # printing content of file we created above.
-rw-rw-r-- 1 daniel daniel 35 Apr 15 01:22 file-from-stdin
$ cat file-from-stdin
I read this from stdin
end of file

4. clear – clears the terminal screen.

clear is self-explanatory, it clears the terminal display and places your cursor at the top left corner. Similar to “cls” command in DOS/Windows/PowerShell.

Use rmdir to delete the named directory, not its contents. To completely wipe out a directory and its contents use ‘rm -r’.

6. mkdir – make or create one or more directories.

mkdir is used to create one or more directories under current directory if no directory argument is given. The user creating the directory must have the permission to create a directory under the specified directory.

When you run a Linux command and pipe it through grep, the grep text itself is shown in the output as well. Once common technique is to use “grep -v” to exclude it. But here is a handy tip which excludes the grep text by placing the first character in a parenthesis –

In Linux, it is very common to expect the files in the system to follow certain naming conventions – such as no white space, usually only lower cases, alphanumeric with underscore or dashes. But in some cases, you will find files which don’t follow this convention – the files might have been copied from other OSes such as Microsoft Windows or MacOS. Here is a trick to empty these files without deleting them.

Use the “truncate” command to empty files with non-standard names.

Requirement – empty files with white space in file name. Keep the files, just reduce the size to 0.

updatedb is usually has a daily cron job to update the default database(‘/var/lib/mlocate/mlocate.db’). To manually update the database, you can manually run the ‘updatedb’ command first. That will take a while depending on the number of files you have on your system, the last time updatedb ran or other file related changes.

First time – update the default database, run any of the below command depending on your requirements. Most likely, the first and/or third command is what you need.

Customizing updatedb
updatedb can be customized to output the search database to a different file than the default db, in addition to this we can change the directory to index other than the default root tree. We can then tell locate to use the custom db.

In the below example, I am indexing the files under home directory in /tmp/home.db database, and then run locate to use this custom DB. As you can see the number of files and directories is way lower and thus the search much faster although since it has to scan specific directory.

Infoblox provides a product to manage your DNS, DHCP and IPAM through a single management interface. In this short article, I will walk you through automating some of the day to day operations work in managing DNS using Infoblox REST API. The REST based api tool can be also used to manage DHCP and IPAM.

The Infoblox WAPI is the REST interface we will interact with. In a highly available DNS setup, the WAPI requests go to the HA Grid Master IP or hostname. The requests typically have arguments and body. A great resource that helped me get started is a github repo of Infoblox Api python modules.

If you can’t find the particular method in the infoblox module, it should’t be difficult to write one. Follow the api reference documentation on the structure of the WAPI Api calls.

Note – in some cases, you have to make multiple api calls to perform certain tasks. One example is updating the TTL for a DNS entry. On the first call, you need to get the host reference id and on second call update the TTL. The below example shows a simple python script to update the TTL (in seconds) for an existing FQDN entry.